Up to now, as everyone knows, the Long Term Evolution (LTE) system is deployed in licensed carriers for operation. However, with the evolution of the LTE system, in the second half of year 2013, some companies (such as America Qualcomm Corporation) put forward a suggestion of carrying out a study on deployment of the LTE system in unlicensed carriers. However, up to now, it has not been accepted by relevant organizations of LTE and no project has already been established.
Qualcomm Corporation gives the following main project establishment reasons: with the rapid increase of data service, licensed spectrums cannot bear such huge data volume in near future, and thus it is suggested to consider deploying LTE in unlicensed spectrums and sharing data traffic in licensed carriers through unlicensed spectrums.
Unlicensed spectrums have many advantages, which are mainly reflected as follows:
1. It is free/low-cost. Since unlicensed spectrums do not need to be purchased, the cost of unlicensed spectrums is almost zero.
2. Admission requirements are low and the cost is low. Individuals and enterprises can participate in deployment and devices of any device manufacturers may be used.
3. Resources can be shared. When multiple different systems operate in the same unlicensed spectrum or different operators of the same system operate in the same unlicensed spectrum, some resource share modes may be used and thereby the efficiency of the spectrums can be improved.
4. Wireless access technologies are many. The operation across different communication standards can be realized, it is difficult to realize collaboration and network topologies are diversified.
5. Wireless access stations are many. The number of users is great. The collaboration difficulty is great. The centralized management overhead is great.
6. Applications are many. Many services such as Machine to Machine (M2M) service and Vehicle to Vehicle (V2V) service may operate in unlicensed spectrums.
The above-mentioned basic features of the unlicensed spectrums decide that the utilization of the unlicensed spectrums may be an important evolution direction of wireless communication systems. However, at the same time, many problems also exist. For example, various wireless systems may exist in unlicensed spectrums, the wireless systems are difficult to coordinate and the interference is serious.
If LTE is deployed in unlicensed carriers, the control of unlicensed carriers still needs to be supported. Most countries require that a listen-before-talk mechanism needs to be supported when communication systems are deployed in unlicensed carriers. Interference caused to neighboring systems for a reason that the neighboring systems simultaneously use unlicensed carriers can be avoided through the listen-before-talk mechanism. Further, a contention mechanism is introduced, i.e., by introducing the contention mechanism to neighboring system stations (generally neighboring stations of the same system), interference caused by a reason that neighboring stations of the same system simultaneously use unlicensed carriers can be avoided.
For an LTE system, when contention is performed in a designed contention window, a base station of LTE may successfully contend for an unlicensed carrier resource at any moment of LTE. In other words, most moments, at which the base station of LTE successfully contends a right to use the unlicensed carrier resource, are not aligned to a start of a subframe of the LTE system, and the base station at most time obtains the right to use the unlicensed carrier at a moment in the middle of a subframe. However, according to the scheduling mechanism of the LTE system, the moment of scheduling always takes subframe as unit and consequently partial incomplete subframes are produced. In order to ensure that the base station can directly use the partial incomplete subframes, the problems how a receiving end rapidly finds that the base station successfully contends for the unlicensed carrier and how the complexity and energy consumption are reduced in a finding process need to be solved.